2) Once the model is finished, what do I have to add to it so it will work in game ? (I am assuming those boxes around the model that are invisible in game). Do |I also have to do anything else apart from add those?

Hi, the best way to create two sided faces is to copy the model, select all polygons of it, and clicking on Modify>Reorient to flip them all. Then you can merge the two together. Be careful that you don't use this too much. Especially for models that don't need it as it will obviously double the polygon count and can create rendering artefacts such as Zfighting.

You'll have to export them to .3ds, which is the only universal 3D format that Zmodeler 1 can import.
.c4d files are Cinema 4D's native project files which can of course only be read by Cinema 4D.
.obj became more common in the years following the release of Zmod1, unfortunately not being implemented in this version for whatever reason.

Things to keep in mind when exporting a model from C4D to zmodeler:
1. each object may only have 1 material applied to it. No more. Otherwise, Zmodeler will only use the first assigned material in the hierarchy on the entire object.
2. filenames for textures may not be any longer than 7 characters. For some reason, Zmodeler cannot automatically import textures that use long filenames, resulting in having to load them in manually. It took me years before I found that out and it still causes frustration till this very day when working with older models.
3. In the export dialog box in C4D, check "Split Discontinuous Points". This is very important if you want materials to show up properly. The downside, the phong shading will be broken at each UV mesh separation. This is barely noticeable at squarish objects, but can become an eyesore in organic shaped objects such as car bodies. Make sure you do not split the UV mesh of each panel during texturing to prevent such smoothing cracks in your mesh.
4. Lastly, ignore any import errors that Zmodeler gives when importing a 3ds file from C4D. It always does that. _________________